The force associated with the one-dimensional potential energy U(x) = a x, where a is a constant, is a. a O b. 2 a x Oc. -2 a x O d. - a Question 21 A force F = (5 i - 3 j) N acts on a particle that undergoes a displacement Ar = (2 i + j) m. What is the work done by the Not yet force on the particle? answered O a.7J O b. 6 J Marked out of 1.50 P Flag question O c. 4J O d. 5 J